The present invention relates to an electroosmotic ink printer, and particularly to a method for operating an electroosmotic ink printer head and an electroosmotic ink printer embodying the method.
Attempts have been made in developing an electroosmotic ink printer for high printing speed operations as shown and described in the aforesaid copending applications. Any one of such printer heads disclosed in the copending applications is adapted for use in the present invention.
A typical example of the disclosed printer head comprises a dielectric support, an array of recording electrodes successively arranged on the support and a porous member disposed on the electrode array in contact with the dielectric support. On the porous member is a mesh electrode on which is disposed a means for supplying ink so that it permeates through the mesh electrode down to the porous member. The porous member has its front edge offset from the front side of the head to which a recording sheet is provided, leaving a portion of the recording electrodes and a portion of the dielectric support to be exposed to the outside. This arrangement provides a beneficial effect on the ink by causing it converge into the forward ends of the recording electrodes.
A circuit is also disclosed which controls the application of modulated potentials simultaneously to the recording electrodes with respect to the overlying mesh electrode. Because of this simultaneous application of potentials, the potential difference between adjacent electrodes is not sufficient under certain circumstances to utilize the converging effect of the ink. This might cause ink dots to spread laterally to adjacent dot positions with the result that the reproduced image is blurred. Additionally, the simultaneous application of potentials tends to produce an excessive amount of ink near the print line posistion. If a turn-off, or disabling voltage is applied to a certain recording electrode following the printing of such excessive ink, a substantial amount of ink must be withdrawn from the print line position. However, part of the ink would inevitably be left, resulting in a smearing of images. Conversely, if a given electrode is disabled successively by continued application of turn-off voltage, a shortage of ink is likely to occur when that electrode is subsequently enabled for printing.
One approach to these shortcomings would be to permanently apply a turn-off voltage to alternate ones of the recording electrodes. However, this is only achieved at the cost of a reduction in image resolution. A second approach would be to provide a plurality of additional electrodes one on each side of the recording electrodes and apply a turn-off voltage to these additional electrodes. However, the increase in total number of electrodes presents difficulties in manufacture and in operation since the additional electrodes would also cause retraction of excessive ink which in turn requires a high voltage to move it forward.